import pandas as pd
import numpy as np

a = pd.DataFrame({"one": pd.Series([1,2,3], index=['a','b','c']), "two": pd.Series([1,2,3,4], index=['a','b','c','d'])})
b = pd.DataFrame({"two": [1,2,3,4], "one": [4,5,6,7]}, index=['c','d','b','a'])

a.fillna(0)
print(a)
print(b)
 
print(a + b)
